1. Field of the Invention
The present invention relates to a plasma information display element such as a plasma display panel (PDP) and a plasma addressed liquid crystal display device (PALC), and a method for producing the same.
2. Description of the Background Art
In recent years, a plasma information display element such as a plasma display panel (PDP) and a plasma addressed liquid crystal display device (PALC) has been attracting public attention.
PDPs are generally classified into those of DC type and those of AC type. At present, AC-type PDPs are the mainstream in view of the discharge stability and the long-term reliability, and AC-type PDPs have already been commercially available.
A structure of a conventional AC-type PDP 300 will be described with reference to FIG. 8. FIG. 8 is a cross-sectional view schematically illustrating the PDP 300. Note that FIG. 8 shows a front substrate 310 in a schematic cross-sectional view taken in a direction that is parallel to the direction in which discharge channels 350 extend, and shows a rear substrate 320 in a schematic cross-sectional view taken in a direction that is perpendicular to the direction in which the discharge channels 350 extend.
The PDP 300 includes the front substrate 310 and the rear substrate 320 provided so as to oppose each other, and a plurality of barrier ribs 340 provided between the front substrate 310 and the rear substrate 320.
The barrier ribs 340 are arranged in a stripe pattern, and the discharge channels 350, which are also arranged in a stripe pattern, are defined each as a space surrounded by the front substrate 310, the rear substrate 320 and the barrier rib 340. This space, i.e., the discharge channel 350, is filled with a discharge gas that can be ionized by a discharge.
The front substrate 310 includes a transparent substrate 312, display electrodes 314 provided on the transparent substrate 312, a dielectric layer 316 provided so as to cover the display electrodes 314, and a protective layer 318 provided on the dielectric layer 316.
The display electrodes 314 of the front substrate 310 are arranged in a stripe pattern and in pairs. One of each pair of display electrodes 314 functions as an anode 314A and the other as a cathode 314C. Moreover, each display electrode 314 includes a transparent electrode 314a and a bus electrode 314b provided on the transparent electrode 314a. 
The rear substrate 320 includes an insulative substrate 322, address electrodes 324 provided on the insulative substrate 322, and a dielectric layer 326 provided so as to cover the address electrodes 324. The address electrodes 324 are arranged in a stripe pattern so as to cross the display electrodes 314, with the barrier rib 340 described above being formed between each pair of adjacent address electrodes 324.
Phosphor layers 328 are formed each in a xe2x80x9cUxe2x80x9d shape on the side surface of the barrier ribs 340 and the upper surface of the dielectric layer 326. Typically, the phosphor layer 328 is a red phosphor layer 328R (e.g., a (Y,Ga)BO3:Eu layer), a green phosphor layer 328G (e.g., a Zn2SiO4:Mn layer) or a blue phosphor layer 328B (e.g., a BaMgAl14O23:Eu layer).
The operation of the PDP 300 having such a structure will be described with reference to FIG. 9. FIG. 9 schematically illustrates the operation of the PDP 300. Note that the PDP 300 has a plurality of picture element regions arranged in a matrix pattern, and a pair of one display electrode 314 and one address electrode 324 intersect each other in each of the picture element regions. Moreover, in a write operation to be described later, one of each pair of display electrodes 314 functions as a scanning electrode.
First, a write discharge is caused selectively in a predetermined picture element region by applying a voltage that exceeds a discharge threshold between one scanning electrode (one of a pair of display electrodes 314) and one address electrode 324. Through the write discharge, a charge is induced/stored around the surface of the dielectric layer 316 above the scanning electrode. Note that such induction/storage of a charge is also referred to as the formation of a wall charge.
Next, a voltage that does not exceed the discharge threshold is applied between a pair of display electrodes 314. At this time, in the predetermined picture element region in which the write discharge has been caused, this voltage is superimposed on a wall voltage that occurs due to the wall charge formed in the write operation, whereby the effective voltage in the region exceeds the discharge threshold, thus initiating a sustain discharge. A predetermined picture element region can be brought into an illuminated state by illuminating the phosphor layer 328 using ultraviolet rays that are generated by the sustain discharge.
In the PDP 300, which operates as described above, the protective layer 318 is provided for the purpose of protecting the display electrodes 314 and the dielectric layer 316 from a discharge (plasma discharge). Typically, an MgO layer is used as the protective layer 318.
Japanese Laid-Open Patent Publication No. 5-234519 discloses a PDP in which the discharge voltage is reduced by using a (111)-oriented MgO layer as the protective layer. Moreover, Japanese Laid-Open Patent Publication No. 10-106441 discloses a PDP in which the anti-sputtering property (the resistance against sputtering due to a plasma discharge) of the protective layer is improved by using a (220)-oriented MgO layer (disclosed as a (110)-oriented MgO layer in the publication) as the protective layer.
However, a (111)-oriented MgO layer, which is provided as the protective layer in the PDP disclosed in Japanese Laid-Open Patent Publication No. 5-234519, does not have a sufficient anti-sputtering property though it has a desirable property for reducing the discharge voltage.
Moreover, a (220)-oriented MgO layer, which is provided as the protective layer in the PDP disclosed in Japanese Laid-Open Patent Publication No. 10-106441 does not have a sufficient property for reducing the discharge voltage though it has a sufficient anti-sputtering property.
The present invention has been made in view of these problems in the art, and has an object to provide a plasma information display element that includes a protective layer with a desirable anti-sputtering property and has a reduced discharge voltage, and a method for producing the same.
A plasma information display element of the present invention includes: a first substrate; a second substrate opposing the first substrate; a plurality of barrier ribs provided between the first substrate and the second substrate; a plurality of discharge channels defined by the first substrate, the second substrate and the barrier ribs; an anode and a cathode provided on one side of the first substrate that is closer to the second substrate; and a protective layer provided so as to cover the anode and the cathode, wherein the protective layer is a layer that contains (220)-oriented MgO and (200)-oriented MgO. Thus, the object set forth above is achieved. Note that xe2x80x9c(220)-oriented MgOxe2x80x9d refers to an MgO crystal in which the crystal plane parallel to the layer plane is the (220) plane, and xe2x80x9c(200)-oriented MgOxe2x80x9d refers to an MgO crystal in which the crystal plane parallel to the layer plane is the (200) plane.
The protective layer may be provided directly on the anode and the cathode.
The plasma information display element may further include a dielectric layer provided between the anode and the cathode and the protective layer.
It is preferred that the protective layer is a layer that is substantially made only of (220)-oriented MgO and (200)-oriented MgO.
The plasma information display element may further include: a third substrate provided so as to oppose the second substrate; and a liquid crystal layer provided between the second substrate and the third substrate.
Each of the discharge channels may further include a phosphor layer.
A method of the present invention is a method for producing a plasma information display element, the plasma information display element including: a first substrate; a second substrate opposing the first substrate; a plurality of barrier ribs provided between the first substrate and the second substrate; a plurality of discharge channels defined by the first substrate, the second substrate and the barrier ribs; an anode and a cathode provided on one side of the first substrate that is closer to the second substrate; and a protective layer provided so as to cover the anode and the cathode, the method including the steps of: preparing the first substrate, in which the anode and the cathode have been formed; and forming the protection layer that contains (220)-oriented MgO and (200)-oriented MgO by depositing an MgO-containing layer so as to cover the anode and the cathode with the first substrate being heated to a temperature of 200xc2x0 C. or more. Thus, the object set forth above is achieved.
Functions of the present invention will now be described.
In the plasma information display element of the present invention, the protective layer, which is provided so as to cover the anode and the cathode, is a layer that contains (220)-oriented MgO and (200)-oriented MgO. Therefore, it is possible to reduce the discharge voltage while suppressing the sputtering of the protective layer by a plasma discharge.
The plasma information display element may further include the dielectric layer provided between the anode and the cathode and the protective layer, or the protective layer may be provided directly on the anode and the cathode. If a structure where the dielectric layer described above is provided is employed, the sputtering of the protective layer is better suppressed, thus improving the reliability of the plasma information display element. If a structure where the protective layer is provided directly on the anode and the cathode is employed, the step of forming a layer (e.g., the dielectric layer described above) between the anode and the cathode and the protective layer can be omitted, thereby reducing the production cost.
In order to reduce the discharge voltage while realizing a desirable anti-sputtering property, it is preferred that the protective layer is a layer that is substantially made only of (220)-oriented MgO and (200)-oriented MgO.
The method for producing a plasma information display element of the present invention includes the step of forming the protection layer that contains (220)-oriented MgO and (200)-oriented MgO by depositing an MgO-containing layer so as to cover the anode and the cathode with the first substrate being heated to a temperature of 200xc2x0 C. or more. Therefore, it is possible to efficiently produce a plasma information display element that includes a protective layer with a desirable anti-sputtering property and has a reduced discharge voltage.
Thus, the present invention provides a plasma information display element that includes a protective layer with a desirable anti-sputtering property and has a reduced discharge voltage, and a method for producing the same.
In the plasma information display element of the present invention, the protective layer, which is provided so as to cover the anode and the cathode, is a layer that contains (220)-oriented MgO and (200)-oriented MgO. Therefore, it is possible to reduce the discharge voltage while suppressing the sputtering of the protective layer by a plasma discharge.
The present invention can suitably be used with a plasma information display element such as a plasma display panel (PDP) and a plasma addressed liquid crystal display device (PALC).